1. Technical Field
The present invention relates to a projection screen, and more particularly to a rear-projection screen for an ultra short throw projector.
2. Background Art
When an image is projected onto a high-gain type screen such as a front-projection screen or a rear-projection screen using a projector, a localized area of high luminance known as a hotspot is generated on the screen. In conventional projectors, such hotspots typically occur on a part of the high-gain type screen which may be relatively close to the projector compared to other areas of the screen, that is, a part of the screen where the angle of incidence of the projected image onto the screen is small.
Thus, for example, in the case of an ultra short throw projector, light exiting from a lens is reflected by a mirror, and then projected at an angle to the screen. Therefore, when an image is projected onto the rear-projection screen, the hotspot is generated at the lower center of the screen image, which corresponds to an area where the projected light having a smaller incidence angle strikes the screen.
The luminance of such hotspots can be reduced by providing a light-diffusing layer or sheet that can diffuse incident light at a part of the screen. Thus, for example, JP-2006-84586-A discloses a technology using a light-diffusing layer or sheet to diffuse incident light to achieve a screen having high gain and a broader viewing angle. In particular, JP-2006-84586-A discloses a front-projection screen composed of a reflecting layer and a light-diffusing layer, in which the light-diffusing layer is disposed on the reflecting layer. The light-diffusing layer diffuses incident light having a specific angular range and transmits incident light having any other angular. Such specific angular range is arranged substantially symmetrically about the optical axis of light exiting the projector, or about a direction perpendicular to the optical axis and a direction perpendicular to the screen.
However, if such a configuration is applied to an ultra short focus projector projecting onto a rear-projection screen, the rear-projection screen passes through most of the incident light at the hotspot. Since the hotspot cannot be eliminated, there is a lot of fluctuation in luminance level.